Climate challenges: can plants adapt in time?

Abstract

The Earth's climate has continuously fluctuated throughout its recent history, with many of the most significant changes linked to changing levels of atmospheric CO2 and other greenhouse gases such as N2O and CH4 during cycles of glacial and interglacial periods (roughly every 100 thousand years since the Mid-Pleistocene). However, the current rise in CO2 is mainly due to human activities and is unprecedented in both its speed and concentration, now exceeding 400 ppm which is well above the ~ 300 ppm seen in the interglacial periods before anthropogenic pollution. This rapid increase in CO2 levels is far beyond what organisms have experienced over the last million years and poses serious challenges to their existence and functioning.While plants thrive under rising CO2 levels (Ainsworth and Long 2021), rapid and continuous warming consequent to greenhouse gases accumulation could push the Earth into a "hothouse" state (Steffen et al. 2018). Rising temperatures, along with concurrent stresses such as prolonged or recurrent droughts and soil salinization, threaten global agricultural productivity, and food security.Organism enduring permanent or recurrent stresses associated with climate change may: a) adapt to the stress; b) migrate to areas more suitable for growth and reproduction, or, in absence of any of these two responses, c) undergo extinction.Plants are sessile organisms. They can migrate through trans-generation seed dispersal, but this process is very slow, limited, and inefficient. Despite observed migration of plant communities in response to warming climates many plants have limited options for migration. Moreover, only migration at speeds greater than one km per year would allow plants to successfully escape the impacts of climate change, as suggested by Corlett and Westcott (2013). The success of the plant migration strategy to cope with climate change is therefore clearly limited.Eliminato: 1 Plants possess the ability to adapt to a wide range of environmental conditions due to their phenotypic plasticity. However, the phenotypes of plants also react rather slowly to environmental pressures. Indeed, any environmental change needs to be sensed first by plants, subsequently activating transcriptional, post-transcriptional or even epigenetic regulatory mechanisms. Those responses lead to phenotypic changes associated with improved tolerance and/or resilience, or with the capacity to escape incoming stress. Is this fast enough to cope with the current pace of climate warming? Previous studies cast doubts on this capacity (Loarie et al. 2009;Ostra et al. 2018). Indeed, a fundamental assumption of paleoecology has been that the rate of evolution is far slower than the rate of current climate change and the faster it occurs, the more extreme phenotypes in populations will likely be lost (Davis et al. 2005) (Figure 1).Additionally, farming might have eroded the capacity for high phenotypic plasticity of agricultural (domesticated) plants. For example, breeding exclusively for high productivity selects for traits that enhance crop yields (e.g. shorter stems, increased fruit and seed size or production). At the same time, it selects against other traits that positively influence plant survival, such as the synthesis of secondary metabolites, including phenolics, which reduce growth and/or produce antinutrients). As a result, plants loose crucial adaptation strategies, leaving them more vulnerable to the impacts of climate change, and to the loss of biodiversity.To allow plants to effectively and timely adapt to climate change may require a "help" from our side. In their Frontiers in Science lead article, Palmgren and Shabala (2024) discuss current knowledge about the possibility of reintroducing lost traits from wild relatives of cultivated plants (re-wilding) or, alternatively, of de novo domestication of wild plants.However, adaptation to abiotic stresses by re-wilding plants probably requires re